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8.12: Blizzards

Difficulty Level: Basic Created by: CK-12
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Where are the snowiest cities in the United States?

Eight of the top ten cities with the highest average snowfall are in upstate New York. This region gets so much snow because it is on the leeward side of the Great Lakes. The area receives lake-effect snow. If you plan to visit in winter, strap on your snow shoes!

Winter Storms

Like hurricanes, winter storms develop from cyclones. But in the case of winter storms, the cyclones form at higher latitudes. In North America, cyclones often form when the jet stream dips south in the winter. This lets dry polar air pour south. At the same time, warm moist air from the Gulf of Mexico flows north. When the two air masses meet, the differences in temperature and pressure cause strong winds and heavy precipitation. Two types of winter storms that occur in the U.S. are blizzards and lake-effect snow storms.

Blizzards

A blizzard is a snow storm that has high winds. To be called a blizzard, a storm must have winds greater than 56 kilometers (35 miles) per hour and visibility of ¼ mile or less because of wind-blown snow. You can see a blizzard in Figure below .

Blizzard in Washington, D.C. Blizzards are unusual in Washington, D.C. Do they ever occur where you live?

Blizzards are dangerous storms. The wind may blow the snow into deep drifts. Along with the poor visibility, the snow drifts make driving risky. The wind also makes cold temperatures more dangerous. The greater the wind speed, the higher the windchill. Windchill is what the temperature feels like when the wind is taken into account. It depends on air temperature and wind speed, as you can see in Figure below . Higher windchill will cause a person to suffer frostbite and other harmful effects of cold sooner than if the wind isn't blowing.

Windchill temperatures may be very low in blizzards because of the high wind speeds. How long does it take for frostbite to occur when the air temperature is 0° F and the wind speed is 55 miles per hour?

Lake-Effect Snow

Some places receive very heavy snowfall just about every winter. If they are near a lake, they may be getting lake-effect snow . Figure below shows how lake-effect snow occurs. Winter winds pick up moisture as they pass over the relatively warm waters of a large lake. When the winds reach the cold land on the other side, the air cools. Since there was so much moisture in the air it can drop a lot of snow. More than 254 centimeters (100 inches) of snow may fall in a single lake-effect storm!

Lake-effect snow falls on the east side of lakes in North America. These snows are heaviest on the east sides of the Great Lakes.

Vocabulary

  • blizzard : A large snow storm with high winds.
  • lake-effect snow : Extreme snowfall caused by the evaporation of relatively warm, moist air into a cold front. The storm drops its snow on the leeward side of the lake.

Summary

  • Blizzards are often part of a mid-latitude cyclone. The jet stream brings cold air into contact with warm moist air.
  • The difference in pressure between the air masses brings about strong winds.
  • Cold polar air absorbs moisture as it travels over the Great Lakes. The air and then dumps snow downwind. This creates lake-effect snow.

Practice

Use this resource to answer the questions that follow.

Science of a Blizzard at http://www.history.com/videos/science-of-a-blizzard (2:03)

  1. What is a blizzard?
  2. What is the wind speed of a blizzard?
  3. What causes a whiteout?
  4. When do blizzards usually occur?
  5. Where are blizzards most common?
  6. What was the deadliest blizzard in history?

Review

  1. Under what circumstances does a blizzard form?
  2. What causes lake-effect snow?
  3. What is a blizzard?

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Description

Difficulty Level:

Basic

Concept Nodes:

Grades:

6 , 7

Date Created:

Jan 04, 2013

Last Modified:

Oct 06, 2014
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